Processes have been developed for the partial oxidation of various liquid, solid and gaseous hydrocarbonaceous feeds, e.g., methane, residual oil, coal, etc., with an oxygen-containing gas to produce synthesis gas, i.e., a gas containing primarily hydrogen and carbon monoxide. The product synthesis gas contains significant amounts of free carbon in the form of soot, particularly when heavy hydrocarbons are employed as feedstock. Various processes have been developed for the separation and recovery of this soot. One method involves scrubbing or quenching the product gas with water to produce a water-soot slurry. The slurry is then treated with a liquid organic extractant, e.g., naphtha, to produce a phase separation, i.e., water and naphtha-soot phases. The naphtha-soot phase is then treated to separate and recover the naphtha and soot. Descriptions of such processes can be found in U.S. Pat. Nos. 2,992,906; 3,473,903; 3,694,355 and 3,917,569.
In these processes the phase separation usually takes place in a decanter. The aqueous phase from the decanter, which contains dissolved gases, naphtha and suspended solids is fed into a flash column wherein the dissolved gases are flashed off overhead and, for reasons of economy, the water recovered for recycle to the scrubbing or quenching step.
U.S. Pat. No. 4,141,695 discloses the use of a flash column for water recovery in such a process. This column not only removes the dissolved gases, but concentrates the suspended solids in a portion of the water which portion is then purged.